Transport apparatus

ABSTRACT

Automatic transport apparatus, especially a gantry crane, provided with a magnet beam for lifting and transporting steel sheets in a sheet stack. From the magnet beam a series of interspaced magnet beam sections is suspended, the sections being situated in an oblique plan forming an angle to the surface of the sheets in the sheet stack. The transport apparatus is able to lift the topmost sheet of a stack of sheets containing large sheets of various lengths, widths, and thicknesses. Each section has an oblong magnet which is pivotally journalled around a horizontal axis and is capable of activating a micro-switch.

United States Patent Hahne Apr. 23, 1974 TRANSPORT APPARATUS 3,486,78412/1969 Ejlertsen 294/655 [75] Inventor: Gustav Adolf Hahne, Oelstykke,

Denmark Primary Examiner-Gerald M. Forlenza Assistant Examiner-George F.Abraham [73] Assignee: H. Nielsen & Son Maskmfabrik AlS, Attorney Agentor Firm Bmwne Beveridge,

Herlev, Denmark Grandi & Kline [22] Filed: Jan. 5, 1973 [21] Appl. No.:321,402 [57] ABSTRACT Automatic transport apparatus, especially a gantry[30] Foreign Application Priority Data crane, provided with a magnetbeam for lifting and Jun. 6, 1972 Great Britain 712/72 transportingsteel Sheets in a Sheet stack' From the magnet beam :1 series ofinter-spaced magnet beam [52] US. Cl. 214/85 D, 214/] BT, 214/658, tiOnsis suspended, the sections being situated in an 294/655 oblique planforming an angle to the surface of the 1511 1111.01. B66c 1/04 Sheetsthe Sheet stack- The transport apparatus is 5 Field of Search n 214 5 D,1 BS 1 BTy able to lift the topmost sheet Of a stack Of sheets COD-214/658; 294/655 taining large sheets of various lengths, widths, andthicknesses. Each section has an oblong magnet which [56] ReferencesCited is pivotally journalled around a horizontal axis and is UNITEDSTATES PATENTS capable of activating a micro-switch.

2,565,927 8/1951 Morgan 214/1 BT X 12 Claims, 9 Drawing Figures mm mm mm5 g m .W4 E m, WMHL i y 3 8 E T'ATENTED APR 2 3 I974 PATENTEBAPR 23 I9748 805; 978

saw 2 [IF 5 T ATENTED APR 2 3 $974 SHEET 4 OF 5 JAHENTEMW 23 5% WEE? 5[INF 5 TRANSPORT APPARATUS The invention relates to a transportapparatus, especially a gantry crane, provided with a magnet beam forlifting and transporting sheets of magnetizable material, especiallysteel sheets, which magnet beam has a girder and at least one from thegirder by means of wires suspended magnet beam section, which has aframe with a front and a rear transverse frame part and two sidegoingframe parts, and one or more electro magnets mounted in the frame.

BACKGROUND OF THE INVENTION A transport apparatus a so-called captivatoris known in the form of a wagon with a conveyor and a magnet beam of theabove-mentioned kind, arranged to be capable of lifting single sheetsfrom a stack of sheets. Such lifting of single sheets is needed inshipbuilding yards, rolling mills and other undertakings where sheetsare processed. Such a transport apparatus with a magnet beam is to bedesigned in such a way that the carrying capacity of its lifting magnetdevice may be adjusted to the thickness of the sheets as this carryingcapacity is partly to be sufficiently strong for attaching the thickestsheet in the stack, partly so poor that it does not attract two sheetslying on top of each other simultaneously. The abovementioned captivatorhas two substantial drawbacks. First it is not capable of lifting allsheets, especially not short thick and long thick sheets. Secondly thecaptivator operates relatively slowly since first it has to pull thesheets up on its conveyor.

SUMMARY OF THE INVENTION The purpose of the invention is to provide atransport apparatus, especially in the form of a gantry crane, whichautomatically and safely is capable of lifting the topmost sheet of astack of sheets containing large sheets of various lengths, widths andthicknesses.

The transport apparatus according to the invention is characteristic inthat the magnet beam has a series of interspaced magnet beam sections,the sidegoing frame parts of which are situated in the same planeforming an angle to the surface of the sheets in the sheet stack. Withthe magnet beam sections being thus suspended from an angle in relationto the surface of the sheet stack, is achieved that after the girderwith the magnet beam sections has been lowered down on the sheet stack,the topmost sheet of the sheet stack will, during the following hoistingmovement of the magnet beam horizontally upwards, first be lifted at itsfront end by means of the magnets of the first magnet beam section. Notuntil the first magnet beam section has been lifted up to a certainheight, the magnet beam section lying behind will come to lift thetopmost sheet, and when the latter magnet beam section has been liftedup to a certain height, the next, behindlying magnet beam section willengage in the lifting of the sheet etc. After the topmost sheet has beenlifted up from the sheet stack, the transport apparatus will transportthe sheet towards the desired spot, where the sheet will be laid down bya lowering movement of the magnet beam.

Furthermore the transport apparatus according to the present inventionis characteristic in that the girder is suspended from the transportapparatus in a substantially horizontal position, and that the magnetbeam sections are suspended from the girder by means of wires of variouslengths so that the sidegoing frame parts of the magnet beam sectionsare placed in the same plane forming an angle to the girder. Hereby anoblique suspension of the magnet beam is obtained in a simple manner sothat the sidegoing frame parts of the magnet beam sections form an angleto the surface of the sheets of the sheet stack without the girder beingturned in advance from a horizontal to an oblique position.

In addition the transport apparatus according to the invention ischaracteristic in that the girder is suspended from the transportapparatus in a substantially horizontal position and can be turned inrelation to this position, and that the magnet beam sections aresuspended from the girder by means of wires of the same lengths so thatthe sidegoing frame parts of the magnet beam sections are placed in thesame plane. Hereby it is possible to turn the girder away from itsnormal horizontal position before the magnet beam is lowered down on thesheet stack so that the sidegoing frame parts of the magnet beamsections form an angle to the surface of the sheet stack; and by turningthe girder more or less this angle may be adjusted to a desired value.Furthermore a simple suspension of the magnet beam sections from thegirder is obtained by using wires of the same lengths for thesuspension.

Moreoever the transport apparatus according to the invention ischaracteristic in that the electro magnets of the magnet beam sectionsare magnets of the reversible type (cf. British Pat. No. 1,187,557). Theuse of such reversible type magnets has the advantage that they can beswitched over between two positions, i.e. a first position with themagnets having a maximum carrying capacity, which means that the magnetsare capable of carrying a heavy sheet, and another position with themagnets having a small carrying capacity.

Furthermore the transport apparatus according to the present inventionis characteristic in that the row of magnet beam sections consists of afront magnet beam section, placed at that end of the girder situated atthe greatest distance from the topmost sheet of the sheet stack, and anumber of lifting magnet beam sections lying there behind, that theframe of the front magnet beam section is suspended. just as the liftingoperation begins. from two carrying wires, one carrying wire being fixedto each side of the center of the frame. that one of the carrying wireshas a weight indicator built into it, and that the electro magnets ofthe front magnet beam section can lift at least half of the actual load.Hereby a rough weighing of that sheet which is in engagement with thefront magnet beam section is obtained, since the weight measured by theweight indicator corresponds substantially to a fourth of the weight ofthe sheet and a fourth of the weight of the magnet beam sections lyingbehind, as the weight indicator only measures the weight in one sideofthe front magnet beam section and as the top-most sheet with its oneend rests on the sheet stack and the lifting magnet beam sections reston this sheet. while the front magnet beam section lifts the other endof the sheet. In this way. just before the lifting operation is started.a rough indication is obtained as to whether the sheet in engagementwith the front magnet beam section is a thin or a thick sheet.

An essential feature of the transport apparatus according to theinvention is that each lifting magnet beam section has along its rearframe part an oblong plate magnet which preferably is designed as anoblong reversible-type plate magnet. If, for instance thin sheets are tobe lifted, i.e., thin sheets of a thickness of about 3-4 millimetres, anordinary oblong plate magnet may unintentionally be turned by theunderlying sheets because of its large depth effect. If, on the otherhand an oblong reversible-type plate magnet is used, made according tothe same principle as the round reversibletype magnets described in thepreviously mentioned British Pat. specification No. 1,187,557, theadvantage is achieved that the tractive force of the plate magnet isconcentrated upon the top part of the topmost sheet of the sheet stackwhen the hoisting movement is started. Incidentally, the plate magnet isto be currentcontrolled in such a way that after the hoisting movementhaving been started, the plate magnet is automatically switched from theposition where the tractive force is concentrated upon the topmost sheetto a position where the plate magnet has maximum tractive force.

Another essential feature of the transport apparatus according to theinvention is that the magnet in each lifting magnet beam section ispivotally journalled around a horizontal axis, which is parallel to thefront or rear frame part. Hereby is achieved that an underlying sheetnot to be lifted turns the magnet out of its normal position, suchmovement can be used for activating the measuring means.

A still further essential feature of the transport apparatus accordingto the invention is that each lifting magnet beam section is providedwith a measuring means so arranged that when the magnet of a liftingmagnet beam section during the lifting of the magnet beam is turned anangle in relation to the sidegoing frame part of the lifting magnet beamsection, which angle is equal to the angle, which the sidegoing frameparts of the lifting magnet beam sections in their normal suspensionposition form with the surface of the sheets in the sheet stack, thenthe measuring means concerned will switch-off the current to the magnetof the lifting magnet beam section concerned, and to all the magnets ofthe behindlying lifting magnet beam sections. Hereby is achieved thatonly the front magnet beam sections, the magnet of which is not turnedbecause these magnets are engaged with the topmost sheet, which islifted up, and because the topmost sheet, which is lifted up, isparallel to the sidegoing frame parts of the magnet beam sectionsconcerned will be supplied with current during the lifting operation,thereby keeping the topmost sheet to be lifted. On the other hand, bymeans of the measuring means, the current will be switched-off to themagnet of the frontmost of those lifting magnet beam sections, themagnet of which is turned to an angle in relation to the frame of thelifting magnet beam section, which angle is equal to the angle formed bythe sidegoing frame parts of the magnet beam section in their normalsuspension position to the surface of the sheet stack; and besides thecurrent will be switched-off to all the magnets of the lifting magnetbeam sections positioned behind, whereby the switched-off lifting magnetbeam sections no longer will engage the underlying sheets during thefurther lifting of the magnet beam.

In addition, an essential feature of the transport apparatus accordingto the invention is that the measuring means is a microswitch attachedon the rear frame part magnet positioned behind the rear edge of thesheet to be lifted, and which besides can switch-off the current to allthe magnets of the lifting magnet beam sections positioned behind thefirst mentioned magnet.

Furthermore, an essential feature of the transport apparatus accordingto the invention is that the magnet beam sections are inter-connected bymeans of movable, mechanical coupling links. Hereby is obtained that theindividual magnet beam sections are capable of performing the requisitemovement mutually during the lifting of a sheet.

Moreover, an essential feature of the transport apparatus according tothe invention is that each coupling link consists of hinge platesattached on opposite frame parts of adjacent magnet beam sections, andof hinge pins extending transversely through eyes in the hinge plates.Hereby is achieved a simple and robust coupling link rendering turningbetween two adjacent magnet beam sections possible.

BRIEF DESCRIPTION OF THE DRAWING The invention is further explainedbelow with reference to the drawings in which, I

FIG. 1 shows in perspective an embodiment of a transport apparatusaccording to the invention in the form of a gantry crane with a magnetbeam suspended in an oblique plane and consisting of a number of magnetbeam sections, the coupling links between the sections being deleted forsake of clarity, I

FIG. 2 on a larger scale and viewed from above the front magnet beamsection and a fragment of the magnet beam section lying behind accordingto FIG. 6, the front magnet beam section being imaginably lowered downon the sheet stack,

FIG. 3 diagrammaticly on a smaller scale and viewed from the side thetransport apparatus in FIG. l,

FIG. 4 diagrammaticly on a smaller scale and viewed from the sideanother embodiment of the transport apparatus in FIG. 1, the magnet beambeing situated in a horizontal position,

FIG. 5 the same, the magnet beam being turned an angle,

FIG. 6 diagrammaticly on a larger scale and viewed from the side afragment of an amended embodiment of the magnet beam shown in FIG. 1 atan initial stage of the hoisting movement of the magnet beam, the frontmagnet beam section of the magnet beam lifting up a short sheet,

FIG. 7 the magnet beam shown in FIG. 6 at a later moment when the sheetis lifted free of the sheet stack,

FIG. 8 the magnet beam shown in FIG. 6 during the lifting of a longersheet and FIG. 9 the magnet beam shown in FIG. 6 during the lifting of along sheet.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a transportapparatus in the form of a gantry crane consisting of two portals 57 and58, a girder 59, combining the two portals, and a magnet beam 60, thegirder 62 of which is suspended from the girder 59 by means of wires 61.The portals 57 and 58 have at the foot travelling wheels (not shown),which, in relation to the longitudinal direction of the girder 62, canrun on longitudinal or athwart rails (not shown). The gantry crane hasrun over a sheet stack 73, consisting of a number of steel sheets, thelengths, widths and thicknesses of which may vary. The magnet beam 60consists of a traverse or girder 62 and a series of interspaced magnetbeam sections 63, 64, 65, 66, 67, 68, 69, and 70, which by means ofwires 97 are suspended from the girder 62.

As shown in FIG. 2 each magnet beam section 63, 64 has a frame 1 whichconsists of a front transverse frame part 2, a rear transverse framepart 3 and two sidegoing frame parts 4 and 5, which frame parts 2-5 cane.g. be U-shaped sectional irons.

In the embodiment of the transport apparatus shown in FIGS. 1 and 3 thewires 97 of the magnet beam sections 63 70 are of various lengths, sothat the sidegoing frame parts 4, 5 of the magnet beam sections areplaced in the same plane forming an angle 7 with the girder 62 saidgirder 62 being suspended from the girder 59 of the gantry crane in asubstantially horizontal position. Since the girder 62 is parallel tothe sheet stack 73. said angle is equal to the suspension angle beta.i.e.. the angle which is formed by the side-going frame parts 4, 5 ofthe magnet beam sections 63-70 in their suspension position to thesurface of the sheets in the sheet stack 73. By using wires 97 ofvarious lengths as shown in FIG. 1 an oblique suspension of the magnetbeam sections 63-70 is obtained without it being necessary to turn thegirder 62.

In FIG. 4 another embodiment of the transport apparatus is shown which,e.g., as shown may be formed as a gantry crane. The girder 62 issuspended from the girder 59 of the gantry crane and is in FIG. 4 in ahorizontal position. In contradiction to the girder 62, shown in FIG. 1,the girder 62 in FIG. 4 may turn in relation to its horizontal position,one end of the girder 62 is lifted or lowered in relation to the otherend. This lifting or lowering can, e.g., be carried out by two hoistingmachineries (not shown), which are mounted on the girder 59 andwhich canoperate independently. The magnet beam sections 63-70 are suspended fromthe girder 62 by means of wires 97 of the same length, so that theside-going frame parts 4 of the magnet beam sections 63-70 are in thesame plane.

In order that the side-going frame parts 4, 5 of the magnet beamsections 63-70 may form an angle ,8 with the surface of the sheets inthe sheet stack 73, the girder 62 is turned from its normalnon-operative position to the turned working-position shown in FIG. 5 bymeans of the hoisting machineries. Hereafter the girder 62 is lowereddown on the surface of the sheet stack 73 and lifting of the topmostsheet can be started.

By the embodiment shown in FIGS. 4 and 5 it is obtained that the angle)3 which the side-going frame parts 4, 5 of the magnet beam sectionsform with the surface of the sheet stack 73, can be adjusted to adesired value. The suspension angle B may thus be varied incontradiction to the embodiment in FIG. 3 where the suspension angle 5has a fixed value. By using wires 97 of the same length as shown in theembodiment according to FIGS. 4 and 5 a very simple suspension of themagnet beam sections 63-70 from the girder 62 is obtained.

The series of magnet beam sections 63-70 consists of a front magnet beamsection 63 and a number of lifting magnet beam sections 64-70 lyingbehind. The front magnet beam section 63 is placed at the end of thegirder 62 situated at the greatest distance from the topmost sheet 78 inthe sheet stack 73.

The individual magnet beam sections 6370 have expediently a width, whichis smaller than the width of the narrowst sheet in the sheet stack 73.

In FIG. 6 a fragment of the magnet beam 60 of FIG. 1 is showndiagrammaticly, viewed from the side during the lifting of a short sheet78.

The magnet beam section 63 shown in FIG. 1, 2 and 6 has an oblongplate-magnet 15 at its front end and an oblong plate-magnet 21 at itsrear end. The platemagnets 15 and 21 can, e.g., each be replaced by oneseries of circular magnets of the reversible type as described in thepreviously mentioned British Pat. specification No. 1,187,557, e.g.,three magnets in each series. The rearmost magnet 21 is pivotallyjournalled around a horizontal axis 114 going through the center pointof the topside of the magnet 21. Between the magnets 15 and 21 one orseveral circular or oblong magnets may be mounted so that the electromagnets of the front magnet beam section 63 can lift at least half ofthe actual load, i.e., the heaviest sheet which is to be lifted by thetransport apparatus, and half of the lifting magnet beam sections lyingbehind.

Each of the lifting magnet beam sections 64, 65, can along each rearframe part have a series of circular magnets 81 (FIG. 1). e.g.. of thereversible type. or as shown in the amended embodiment in FIG. 6 anoblong plate magnet 100. This oblong plate magnet 100 is expedientlydesigned as an oblong plate-magnet of the reversible type. The use orthis type of magnets has the advantage that said magnets can be switchedover between two positions,

i.e., a first position with the magnets having a maximum carryingcapacity, which means that the magnets are capable of carrying a heavysheet, and another position with the magnets having a reduced carryingcapacity so that the transport apparatus is capable of lifting thinsheets.

If, e.g., thin sheets are to be lifted, i.e., thin sheets of a thicknessof about 3-4 mm an ordinary oblong platemagnet 100 may unintentionallybe turned by the underlying sheets because of its large depth effect.If, on the other hand, an oblong plate-magnet 100 of the reversible typeis used, said magnets being made according to the same principle as thecircular magnets described in the previously mentioned British Pat.specification No. 1,187,557, the advantage is achieved that the tractiveforce of the plate-magnets is concentrated upon the top part of thetopmost sheet of the sheet stack, when the hoisting movement is started.Incidentally, the plate magnet is to be current-controlled in such a waythat after the hoisting movements having been started the plate-magnetis automatically switched from the position where the tractive force isconcentrated upon the topmost sheet to a position where the plate-magnethas maximum tractive force.

As it appears from FIGS. 2 and 6 the frame 1 of the front magnet beamsection 63 is suspended from two carrying wires 95, one carrying wirebeing fixed to each side of the centre of the frame 1. At a suitablespot a weight indicator 38 (cf. FIG. 2) is built into one of thecarrying wires 95. By means of such a weight indicator 38 a roughweighing of the sheets is obtained with which the front magnet beamsection 63 is in engagement. This is possible, since the weight measuredby the weight indicator corresponds substantially to a fourth of theweight of the sheet and a fourth of the weight of the magnet beamsections lying behind, as the weight indicator only measures the weightin one side of the front magnet beam section 63 and as the topmost sheetwith its one end rests on the sheet stack 73 and the lifting magnet beamsections 64-70 rest on this stack. while the front magnet beam section63 lifts the other end of the sheet. In this way just before the liftingoperation is started a rough indication is obtained whether the sheet,with which the front magnet beam section is in engagement, is a thin ora thick sheet.

Each of the oblong plate-magnets 100 in the embodiment according to FIG.6 is pivotally joumalled around a horizontal axis 83 which is parallelto the front or rear frame part 2 respectively 3 (FIG. 2). Hereby it isobtained that an underlying sheet not to be lifted turns the magnet 100out of its normal position in relation to the side-going frame part 4,said movement can be used for activating a measuring means 84 mentionedbelow.

The oblong magnets and 21 in the front magnet beam section 63 ispivotally joumalled around end journals 113 respectively 114 (FIGS. 2and 6) mounted in holes in the side-going frame parts 4 and 5. Eachlifting magnet beam section, for instance 64, has a measuring means,especially a micro-switch 84 (FIG. 6), so arranged that when the magnets100 during the lifting of the magnet beam section 63 are turned an anglein relation to the sidegoing frame parts 4 of the lifting magnet beamsection 64, which angle is equal to the suspension angle of the liftingmagnet beam sections in the girder 62, then the micro-switch 84 willswitch off the current to the magnets 100 in the lifting magnet beamsection 64 and to all the magnets 100 in the lifting magnet beamsections 65,66, 70 lying behind. Hereby is achieved that only the frontlifting magnet beam sections or the front lifting magnet beam section 64(in FIG. 9), the magnets 100 of which are not turned because thesemagnets 100 are engaged with the topmost sheet 78, which is being liftedup, and because the topmost sheet 78" is parallel to the sidegoing framepart 4 of the lifting magnet beam sections or the lifting magnet beamsection 64 concernedwill be supplied with current during the liftingoperation, thereby holding the topmost sheet 78 to be lifted. On theother hand, the current will be means of the micro-switch 84 designed asa measuring means be switched-off to the magnets 100 of that liftingmagnet beam section 65, the magnet 100 of which is turned an angle inrelation to the sidegoing frame part of the lifting magnet beam section.which angle is equal to the suspension angle of the magnet beam sectionin the girder 62; and besides the current will be switched-off to allthe magnets 100 in the lifting magnet beam sections 66,67, 70 lyingbehind, whereby the currentless lifting magnet beam section 65 no longerwill seize the underlying sheets during the lifting of the magnet beam62.

The micro-switch 84 is placed on the rear frame part of each liftingmagnet beam section and activated by a spring 85 (FIG. 6) connected withthe magnet 100. Hereby is achieved in a simple and reliable way anactivation of the micro-switch 84 when the magnet 100 is turned. Insteadofa micro-switch, for instance a photoelectric cell or an inductivefeeler or a potentiometer which produce a voltage proportional to theangular motion of the magnets can be used as a measuring means.

The magnet beam sections 63,64, are interconnected by means of movable,mechanical coupling links 99 as shown in FIGS. 2 and 6. Hereby isensured that the individual magnet beam sections 63,64, 70, during thelifting of a sheet, can perform the mutual movements required. Eachcoupling link 99 consists preferably of two hinge plates 101 and 102,positioned on opposite frame parts 2 and 3 of adjacent magnet beamsections, such as for instance 63 and 64 in FIG. -6, and one hinge pin 103 extending through eyes in the hinge plates 101 and 102. The couplinglink 99 renders a robust and simple coupling link possible ensuring thatturning can take place between two adjacent magnet beam sections.

The carrying wires (FIG. 6) of the front magnet beam section 63 are attheir top ends connected with a pressure spring 96, placed in the girder62. The wires 97 from which the magnet beam sections 63-70 are suspendedare at their top ends connected with a pressure spring 98 mounted on thegirder 62. By giving these springs 96 and 98 a suitable pre-stressing,it is possible to regulate the length of the individual wires 95 and97so that the sidegoing frame part 4 of the individual magnet beamsections come in the same oblique level, and so that the underside ofthe frame part 4 is on the same level. Thus it is possible to allow forinaccuracies arising from ordinary wear and tear during the use and,from the manufacture of the individual magnet beam sectionsor-inaccurate suspension during the mounting of the magnet beamsections. An accurate suspension ensures that the individual magnet beamsections participating in the lifting of the topmost sheet 78 or 78' or78", essentially come to carry the same weight.

LIFTING OF A SHORT SHEET ACCORDING TO FIGS. 6 AND 7 Automatic lifting ofa short sheet 78, the length of which is equal to about the length of amagnet beam section, is done in the following way. The girder 62 withthe magnet beam sections 63,64,65, 70 is lowered down on the sheet stack73. Full voltage is switched-on to all the magnets 15,21 and of themagnet beam sections. Then the girder 62 starts the hoisting movement.After a certain hoisting movement of the girder 62, the magnet beamtakes up the position shown in FIG. 6. The front magnet beam section 63is turned and lifted forming an angle, which is equal to the suspensionangle B. By a further hoisting movement not only the front magnet beamsection 63 will be lifted, but also the front lifting magnet beamsection will be lifted at its front end because of the coupling link 99"1511566556of"; continuous hoisting movement the oblong plate magnet100, engaged with the topmost sheet but one 77, will be turned inrelation to the lifting magnet beam section 64. In FIG. 7 the magnetbeam is lifted so much that the oblong plate magnet 100 of the liftingmagnet beam section 64 has turned an angle which is equal to thesuspension angle beta. Thereby the micro-switch 84 is activated by thespring 85, whereby the current to the oblong plate magnet 100 isswitched-off and to the behindlying plate magnets 100 in the liftingmagnet beam section 65,66, 70. Through the further hoisting movement thelifting magnet beam sections 65,66, 70 are lifted in succession up fromthe sheet stack 73. When all the lifting magnet beam sections 64-70 havebeen lifted up from the sheet stack 73, the gantry crane transports thesheet 78 to the desired location where the sheet 78 is laid down by alowering movement of the girder 62.

LIFTING OF A LONGER SHEET ACCORDING TO FIG. 8.

The automatic lifting of a longer sheet 78 (FIG. 8), i.e., a sheet, thelength of which is one and a half times the length of a magnet beamsection, proceeds in the same way as described above in connection withthe lifting of the short sheet 78 in FIGS. 6 and 7. The position of themagnet beam shown in FIG. 8 corresponds to the position shown in FIG. 7.

LIFTING OF A LONG SHEET ACCORDING TO FIG. 9

With reference to FIG. 9 showing the lifting of a long sheet 78 all theoblong plate magnets 100 are switched-on as thin plate magnets duringthe initial stage of the lifting of the topmost sheet 78". If themicro-switch 84 of the lifting magnet beam section 64 is not activated,when the lifting magnet beam section 64 is lifted up clear of the sheetstack 73, full current intensity is switched-on to the oblong platemagnet 100 in the lifting magnet beam section 64.

The weight indicator 38 serves as mentioned above to ascertain whether athin or a thick sheet is placed under the magnet beam. Hereby the weightindicator 38 ensures that the used magnets 15,21, 100 of the reversibletype are switched-on to either the thin plate function or the thickplate function, i.e., that the magnets function either as thin platemagnets or as thick plate'magnets (strong magnets). First the case isconsidered where a thin sheet is placed under the magnet beam. When theweight indicator 38 has indicated that a thin sheet is concerned, allthe magnets 15,21,100 are switched-on as thin plate magnets. Thereafterthe depth of the magnetic field is not greater than the thickness of thethin sheet. By lifting the magnet beam is hereby avoided that the magnetpicks up more than the topmost sheet. When the magnet beam has beenmoved a few centimetres up above the surface of the sheet stack 73, themagnets 15,21,100 are switched-on to thick plate function for purposesof security.

Thereafter the case is considered where a thick sheet is placed on topof the sheet stack 73. When the weight indicator 38 has ascertained thata heavy sheet, and consequently a thick sheet is concerned, the magnets15,21,100 are switched-on to thick plate function. Hereby is avoidedthat the magnet beam will lift two or more sheets because the magneticfield does not extend beneath the underside of the thick sheet.

The gantry crane according to the invention with the oblique suspendedmagnet beam sections renders it possible to lift one sheet at a timefrom a buffer stack in which steel sheets of arbitrarily large lengthhave been stacked. Such sheet stacks are for instance found in sheetstores at shipbuilding yards.

A characteristic of the lifting operation of the magnet beam is that asheet, when lifted, is first lifted up by its front edge.

Since a sheet lifted up by means of the magnets invariably will flushwith the longitudinal frame parts of the magnet beam sections, thissheet cannot cut-out (switch-off the current to) the magnets which areto remain switched-on as the switch-off of the current to the magnetsonly will happen when a magnet takes up a position in which this isturned an angle equal to the suspension angle ['1 in relation to theframe of the magnet beam section concerned. The turned position of themagnet is characteristic of the process of lifting of a sheet. Theturned position will only occur when an underlying sheet, not to belifted, turns the magnet out of its normal position, whereby themicro-switch belonging to the magnet is activated and the magnet currentswitched-off.

The present invention is not limited to the embodiments shown anddescribed but can be modified in many ways within the scope of thesucceeding claims.

I claim:

1. A transport apparatus, especially a gantry crane, provided with amagnet beam for lifting and transporting sheets of magnetizablematerial, especially steel sheets,from a stack of sheets which magnetbeam has a girder and a series of spaced beam sections suspended fromthe girder by means of wires, each beam section having a frame with afront and a rear transverse frame part and two sidegoing frame parts andone or more electro magnets mounted in the frame, the sidegoing frameparts of each of the beam sections being situated in the same planeforming an angle ([3) to the surface of the sheets in the sheet stack.

2. A transport apparatus according to claim 1, characterized in that thegirder is suspended from the transport apparatus in a substantiallyhorizontal position, and that the magnet beam sections are suspendedfrom the girder by means of wires of various lengths so that thesidegoing frame parts of the magnet beam sections are placed in the sameplane forming an angle (y) to the girder.

3. A transport apparatus according to claim 1, characterized in that thegirder is suspended from the transport apparatus in a substantiallyhorizontal position and can be inclined relative to this position, andthat the magnet beam sections are suspended from the girder by means ofwires of the same lengths so that the sidegoing frame parts of themagnet beam sections are placed in the same plane.

4. A transport apparatus according to claim 1 characterized in that theelectro magnets of the magnet beam sections are magnets of thereversible type.

5. A transport apparatus according to claim 4, characterized in that theseries of magnet beam sections consists of a front magnet beam section,placed at the end of the girder situated at the greatest distance fromthe topmost sheet of the sheet stack and a number of behind lyinglifting magnet beam sections, that the frame of the front magnet beamsection is suspended from two carrying wires, one carrying wire beingfixed to each side of the centre of the frame, that one of the carryingwires has a weight indicator built into it, and that the electro magnetsof the front magnet beam section can lift at least half of the actualload. 7

6. A transport apparatus according to claim 5, characterized in thateach lifting magnet beam section has along its rear frame part an oblongplate magnet.

7. A transport apparatus according to claim 6, characterized in that theplate magnet is designed as an oblong reversible-type plate magnet.

8. A transport apparatus according to claim 4, characterized in that themagnet in each lifting magnet beam section is pivotally journalledaround a horizontal axis, which is parallel to thefront or rear framepart.

9. A transport apparatus according to claim 4 characterized in that eachlifting magnet beam section is provided with a measuring means soarranged that when the magnet of a lifting magnet beam section duringthe lifting of the magnet beam is turned an angle in relation to thesidegoing frame part of the lifting magnet beam section, which angle isequal to the angle, which the sidegoing frame parts of the liftingmagnet beam sections in their normal suspension position form with thesurface of the sheets in the sheet stack, then the measuring meansconcerned will switch-off the current to the magnet of the liftingmagnet beam section concerned, and to all the magnets of the behindlyinglifting magnet beam sections.

10. A transport apparatus according to Claim 9, characterized in thatthe measuring means is a microswitch attached on the rear frame part ofeach lifting magnet beam section, and which can be activated by a springconnected with the magnet at the rear frame part of the lifting magnetbeam section.

11. A transport apparatus according to claim 1, characterized in thatthe magnet beam sections are interconnected by means of movable,mechanical coupling links.

12. A transport apparatus according to claim 11, characterized in thateach coupling link consists of hinge plates attached on opposite frameparts of adjacent magnet beam sections, and of hinge pins extendingtransversely through eyes in the hinge plates.

1. A transport apparatus, especially a gantry crane, provided with amagnet beam for lifting and transporting sheets of magnetizablematerial, especially steel sheets, from a stack of sheets which magnetbeam has a girder a series of spaced beam sections suspended from thegirder by means of wires, each beam section having a frame with a frontand a rear transverse frame part and two sidegoing frame parts and oneor more electro magnets mounted in the frame, the sidegoing frame partsof each of the beam sections being situated in the same plane forming anangle ( Beta ) to the surface of the sheets in the sheet stack.
 2. Atransport apparatus according to claim 1, characterized in that thegirder is suspended from the transport apparatus in a substantiallyhorizontal position, and that the magnet beam sections are suspendedfrom the girder by means of wires of various lengths so that thesidegoing frame parts of the magnet beam sections are placed in the sameplane forming an angle ( gamma ) to the girder.
 3. A transport apparatusaccording to claim 1, characterized in that the girder is suspended fromthe transport apparatus in a substantially horizontal position and canbe inclined relative to this position, and that the magnet beam sectionsare suspended from the girder by means of wires of the same lengths sothat the sidegoing frame parts of the magnet beam sections are placed inthe same plane.
 4. A transport apparatus according to claim 1characterized in that the electro magnets of the magnet beam sectionsare magnets of the reversible type.
 5. A transport apparatus accordingto claim 4, characterized in that the series of magnet beam sectionsconsists of a front magnet beam section, placed at the end of the girdersituated at the greatest distance from the topmost sheet of the sheetstack and a number of behind lying lifting magnet beam sections, thatthe frame of the front magnet beam section is suspended from twocarrying wires, one carrying wire being fixed to each side of the centreof the frame, that one of the carrying wires has a weight indicatorbuilt into it, and that the electro magnets of the front magnet beamsection can lift at least half of the actuel load sheet.
 6. A transportapparatus according to claim 5, characterized in that each liftingmagnet beam section has along its rear frame part an oblong platemagnet.
 7. A transport apparatus according to claim 6, characterized inthat the plate magnet is designed as an oblong reversible-type platemagnet.
 8. A transport apparatus according to claim 4, characterized inthat the magnet in each lifting magnet beam section is pivotallyjournalled around a horizontal axis, which is parallel to the front orrear frame part.
 9. A transport apparatus according to claim 4characterized in that each lifting magnet beam section is provided witha measuring means so arranged that when the magnet of a lifting magnetbeam section during the lifting of the magnet beam is turned an angle inrelation to the sidegoing frame part of the lifting magnet beam section,which angle is equal to the angle, which the sidegoing frame parts ofthe lifting magnet beam sections in their normal suspension positionform with the surface of the sheets in the sheet stack, then themeasuring means concerned will switch-off the current to the magnet ofthe lifting magnet beam section concerned, and to all the magnets of thebehindlying lifting magnet beam sections.
 10. A transport apparatusaccording to Claim 9, characterized in that the measuring means is amicro-switch attached on the rear frame part of each lifting magnet beamsection, and which can be activated by a spring connected with themagnet at the rear frame part of the lifting magnet beam section.
 11. Atransport apparatus according to claim 1, characterized in that themagnet beam sections are inter-connected by means of movable, mechanicalcoupling links.
 12. A transport apparatus according to claim 11,characterized in that each coupling link consists of hinge platesattached on opposite frame parts of adjacent magnet beam sections, andof hinge pins extending transversely through eyes in the hinge plates.